1. Technical Field
The present invention relates to a method for manufacturing a semiconductor light-emitting apparatus, and particularly to a method for manufacturing an AlGaInP compound semiconductor light-emitting diode (LED) having high light extraction efficiency.
2. Description of the Related Art
Compound semiconductors based on (AlzGa1-z)xIn1-xP (0≦x≦1, 0≦z≦1) (referred to hereinafter simply as AlGaInP-based semiconductors) are capable of emitting light in colors from red to green, and are widely used in light-emitting diodes (LED: Light Emitting Diode), semiconductor lasers (LD: Laser Diode), and other semiconductor light-emitting elements and the like. Usually, layers of these compound semiconductors are epitaxially grown using metal-organic chemical vapor deposition (MOCVD) on a GaAs substrate for lattice matching.
In order to increase the luminance of a light-emitting diode, it is important to improve the efficiency of light extraction from the element. For example, in a layered structure formed by stacking AlGaInP-based semiconductor layers on a GaAs substrate, of the light emitted from the active layer, the light emitted toward the substrate is absorbed by the GaAs substrate, and this absorption leads to decreased light extraction efficiency.
As an example of a conventional technique, Japanese Laid-open Patent Publication No. 2008-98336 (referred to hereinafter as Patent Reference 1) discloses a method whereby a reflective metal layer is provided to a semiconductor light-emitting layer structure grown on a temporary substrate, a metal substrate or other permanent substrate is then affixed thereto, and the temporary substrate, which is a light-absorbing substrate, is removed.
A method is also known for roughening the light extraction surface by forming a relief structure or projections and depressions structure (hereinafter referred to as projection/depression structure) thereon in order to prevent total reflection at the light extraction surface of the light-emitting element from reducing the light extraction efficiency. Known methods for roughening the light extraction surface by forming a projection/depression structure thereon achieve the surface roughening through use of hydrochloric acid, sulfuric acid, hydrogen peroxide, or, as disclosed in Japanese Laid-open Patent Publication No. 2000-299494 (referred to hereinafter as Patent Reference 2), a mixture of these substances (refer to Patent Reference 2, for example). However, when wet etching is used, a satisfactory surface roughening is not necessarily possible to achieve, due to the effects of the crystal properties of the substrate, as well as the crystal-plane direction of the light extraction surface, the composition of the etchant, and other factors. The GaP layer described in the references referenced above is widely used in LED light extraction layers, and anisotropic etching thereof for surface roughening is relatively easy to perform. However, in etching of an AlGaInP-based compound semiconductor, which contains Al, the etching solution and other conditions have significant effects, and the conditions are difficult to adjust. Stable, satisfactory surface roughening is therefore difficult to achieve.
A projection/depression structure can also be formed by dry etching. A sequence of steps is required whereby an insulating film of SiO2, for example, or the like is formed, after which a desired pattern is formed by photolithography or another method, the insulating film is etched, and the semiconductor layer is then etched using the etched insulating film as a mask. The process is therefore complex.